This invention relates to a rotor for a permanent magnet-type dynamoelectric machine, and more particularly to a dynamoelectric machine rotor having a plurality of permanent magnet segments.
FIG. 1 illustrates, in a sectional side view, one example of a permanent magnet-type dynamoelectric machine 10 with the conventional rotor having a segmented rotor magnet assembly. The dynamoelectric machine 10 comprises a housing 11 and a stator 12 mounted to the housing 11 and including a stator core 13 and stator coils 14 wound around the core 13. The dynamoelectric machine 10 also comprises a rotor 15 rotatably supported within the housing 11 by a pair of bearings 16 and 17. The rotor 15 comprises a rotary shaft 18 rotatably supported by the bearings 16 and 17, a tubular cylindrical rotor core 19 press-fitted onto the shaft 18 and a rotor magnet assembly 20. The rotor magnet assembly 20 comprises a plurality of permanent magnet segments 21 attached to a circumferential surface 22 of the rotor core 19 to form a substantially tubular assembly as best seen in FIG. 2. In the illustrated example, the assembly 20 comprises four magnet segments 21 made of a ferrite magnetic material. As shown in FIG. 3, each magnet segment 21 has an inner cylindrical surface 23 extending along the outer circumference 22 of the rotor core 19, an outer cylindrical surface 24, two end surfaces 25, two side surfaces 26 extending axially in a plane containing the axis of the rotor 15, and two axially extending chamferred surfaces 27 at the outer axial side edges or corners of the magnet segment 21. The chamferred surfaces 27 of the magnet segments 21 are provided for reducing the cogging torque and the magnetic noise. The magnet segments 21 are attached to the outer surface 22 of the rotor core 19 by a suitable bonding agent 28. When associated, each of the chamferred axially-extending outer side edges 27 defines, together with the chamferred outer side edge 27 of the adjacent magnet segment 21, a plurality of axial recesses 29 of a V-shaped cross section.
The permanent magnet segments 21 of the rotor magnet assembly 20 of the conventional design are attached only by the bonding agent 28 applied between the inner cylindrical surface 23 of the segments 21 and the outer cylindrical surface 22 of the rotor core 19. Therefore, a massive centrifugal force is exerted on the segments 21, causing a tremendous amount of separating force to be applied to the bonding agent 28. Also, at the time of acceleration or deceleration during the period of starting or stopping, a massive shearing force applies to the bonding agent 28 between the magnet segments 21 and the outer cylindrical surface 22 of the rotor core 19.
Therefore, the dynamoelectric rotor assembly of this type utilizing magnet segments bonded to the rotor core is not suitable to be operated at a relatively high speed rotation or with a repeated stopping and starting operation. If the magnet segment or the fragment thereof is separated due to the centrifugal force during a high-speed rotation, the separated segment is very dangerous as it flies at a great speed. Also the magnet segment or the fragment which is separated from the assembly may be caught between the stator and the rotor, halting or damaging the dynamoelectric machine.